s3op - antisurge training manual

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Title Page

Series 3 PlusAntisurge ControllerTraining Reference Manual

Operations Module 1

Publication S3OP_AS (3.1)

November 2000

© 2001, Compressor Controls Corporation. All rights reserved.

This manual is for the use of Compressor Controls Corporation and is not to be reproduced without written permission.

The impeller and TTC logos, Total Train Control, TTC, Recycle Trip, Safety On, Air Miser, TrainView, and WOIS are registered trademarks; and the Series 5 logo, Reliant, Vanguard, TrainTools, TrainWare, SureLink, Guardian, and COMMAND are trademarks of Compressor Controls Corporation. Other product and company names used herein are trademarks or registered trademarks of their respective holders.

The control methods and products discussed in this manual may be covered by one or more of the following patents, which have been granted to Compressor Controls Corporation by the United States Patent and Trademark Office:

4,486,142 4,494,006 4,640,665 4,949,2765,347,467 5,508,943 5,599,161 5,609,4655,622,042 5,699,267 5,743,715 5,752,3785,879,133 5,908,462 5,951,240 5,967,7426,116,258

Many of these methods have also been patented in other countries, and additional patent applications are pending.

The purpose of this manual is only to describe the configuration and use of the described products. It is not sufficiently detailed to enable outside parties to duplicate or simulate their operation.

The completeness and accuracy of this document is not guaranteed, and nothing herein should be construed as a warranty or guarantee, express or implied, regarding the use or applicability of the described products. CCC reserves the right to alter the designs or specifications of its products at any time and without notice.

The protection provided by this product may be impaired if it is used in a manner not specified by Compressor Controls Corporation.

Contents -1

S3OP_AS (3.1) - Series 3 Plus Operations Antisurge Training Manual

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1.1 Reciprocating Compressors . . . . . . . . . . . . . . . . 1-21.1.2 Rotating Compressors. . . . . . . . . . . . . . . . . . . 1-2

1.2 Operating Map . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1.2.1 Operating Point . . . . . . . . . . . . . . . . . . . . . . 1-41.2.2 Speed Curves . . . . . . . . . . . . . . . . . . . . . . . 1-51.2.3 Performance Limits . . . . . . . . . . . . . . . . . . . . 1-61.2.4 Axes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

1.3 Surge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

1.3.1 Phenomenon . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

1.3.2 Protection Method . . . . . . . . . . . . . . . . . . . . . 1-11

Antisurge Control . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1 Surge Limit Line . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1.1 Axis Selection . . . . . . . . . . . . . . . . . . . . . . . 2-22.1.2 Description of "Surge Limit Line" . . . . . . . . . . . . . 2-52.1.3 Formulas for Hp and Qs . . . . . . . . . . . . . . . . . . 2-62.1.4 S-value "Ss" . . . . . . . . . . . . . . . . . . . . . . . . 2-62.1.5 Speed Characterizer. . . . . . . . . . . . . . . . . . . . 2-7

2.2 Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.2.1 Safety Margin . . . . . . . . . . . . . . . . . . . . . . . 2-92.2.2 S-value . . . . . . . . . . . . . . . . . . . . . . . . . . 2-112.2.3 Flow Characterizer . . . . . . . . . . . . . . . . . . . . 2-12

2.3 "Recycle Trip" Algorithm . . . . . . . . . . . . . . . . . . . . 2-13

2.4 "Safety On" Algorithm . . . . . . . . . . . . . . . . . . . . . . 2-16

2.4.1 Surge Detection using the "Safety On Line". . . . . . . . 2-162.4.2 Surge Detection using a "Surge Signature" . . . . . . . . 2-172.4.3 "Safety On" Response. . . . . . . . . . . . . . . . . . . 2-18

2.5 Summary (Example) . . . . . . . . . . . . . . . . . . . . . . 2-19

Contents -2

February 26, 2001

Antisurge Application Additional Control Functions . . . 3-1

3.1 Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2 Actuator Output Conditioning . . . . . . . . . . . . . . . . . . 3-2

3.2.1 Valve Flow Characterization. . . . . . . . . . . . . . . . 3-33.2.2 Valve Dead Band Compensation . . . . . . . . . . . . . 3-43.2.3 Output Clamps. . . . . . . . . . . . . . . . . . . . . . . 3-53.2.4 Tight Shut-Off . . . . . . . . . . . . . . . . . . . . . . . 3-63.2.5 Output Reverse . . . . . . . . . . . . . . . . . . . . . . 3-63.2.6 Output Tracking . . . . . . . . . . . . . . . . . . . . . . 3-6

3.3 Operating States . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3.3.1 Operating State Transitions . . . . . . . . . . . . . . . . 3-73.3.2 Manual Operation . . . . . . . . . . . . . . . . . . . . . 3-83.3.3 Manual Override . . . . . . . . . . . . . . . . . . . . . . 3-83.3.4 Loop Checks With the Compressor On-Line . . . . . . . 3-10

Series 3 Plus Gains and Biases . . . . . . . . . . . . . . 4-1

Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1Gains and Biases Chart . . . . . . . . . . . . . . . . . . . . . 4-3

Series 3 Plus Antisurge Controller Fallback Strategies . 5-1

Constant Output (Mode fD 31) . . . . . . . . . . . . . . . . . 5-1Minimum Flow Control (Mode fD 32) . . . . . . . . . . . . . . 5-1Default Compression Ratio (Mode fD 33) . . . . . . . . . . . . 5-2Assumed Sigma (Mode fD 34) . . . . . . . . . . . . . . . . . 5-2Fallback Speed (Mode fD 35) . . . . . . . . . . . . . . . . . . 5-2Assumed Vane Angle (Mode fD 36) . . . . . . . . . . . . . . . 5-2Assumed Adjacent Stage Flow Rate (Mode fD 37) . . . . . . . 5-3Alternate K for Valve-Sharing Controllers (Mode fD 38). . . . . 5-3Temperature-Based Polytropic Head (Mode fD 39) . . . . . . . 5-3

Antisurge Application Typical Surge Test Procedure . . 6-1

Background Summary . . . . . . . . . . . . . . . . . . . . . . . 6-1

Surge Testing in AUTOmatic . . . . . . . . . . . . . . . . . . . . 6-2

Surge Testing in MANUAL . . . . . . . . . . . . . . . . . . . . . 6-5

Surge Testing On-Line . . . . . . . . . . . . . . . . . . . . . . . 6-6

Determining Surge Line without Surge Testing . . . . . . . . . . . 6-6

Contents -3

S3OP_AS (3.1) - Series 3 Plus Operations Antisurge Training Manual

Series 3 Plus Antisurge Controller Operating Principles. 7-1

Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2Auxiliary Window . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Series 3 Plus Antisurge Controller Configuration Planner. . . . . . . . . . . . . . . . . FM301/L

Contents -4

February 26, 2001

Introduction 1-1

S3OP_AS_Intro1 Antisurge Application Training Manual

Chapter 1: Introduction

In almost all Petrochemical processes, Compressors are used totransport or compress gasses. Most processes depend on thesecompressors, so it is important that they are operated in areliable fashion. To accomplish this one needs to know as muchas possible of the state in which the machine is running, someasures can be taken to prevent shutdowns and keep thedowntime of not only the compressor but the whole process to aminimum.

This Training Manual describes the main features of theCOMPRESSOR CONTROLS CORPORATION

Control System. In chapter 2 the Antisurge algorithms arediscussed.

1.1Compressors

In the field two basic types of compressors are used: Rotatingand Reciprocating.

©Copyright 1997 Compressor Controls Corporation. All rights reserved. Reproduction by permission only.

Major control system objectives

(user benefits)

1. Increase reliability of machinery and process

• Prevent unnecessary process trips anddowntime

• Minimize process disturbances

• Prevent surge and surge damage

• Simplify and automate startup and shutdown

2. Increase efficiency of machinery and process

• Operate at lowest possible energy levels

• Minimize antisurge recycle or blow-off

• Minimize setpoint deviation

• Maximize throughput using all availablehorsepower

• Optimize loadsharing of multiple units

1-2 Introduction

February 26, 2001

1.1.1ReciprocatingCompressors

The Reciprocating Compressors are Compressors of the Pistontype. They work like a reversed combustion engine and are usedin applications where a very high compression ratio is required.

1.1.2Rotating

Compressors

There are two distinct types of Rotating Compressors: the Axialand the Centrifugal Compressors. Axial Compressors are usedin applications that need high flow rates, while CentrifugalCompressors are used in applications that require a highcompression ratio in combination with lower flow rates.Compressors that combine these two types are also seen. Inthose cases the first few stages of the Compressor are Axial (tocreate high flow rates) and the last few stages are Centrifugal (tobuild up more pressure).

© Copyright 1997 Compressor Controls Corporation. All rights reserved. Reproduction by permission

Centrifugal compressors

• Widespread use, many applications

• Gas is accelerated outwards by rotating impeller

• Can be built for operation as low as 5 psi, or operationas high as 8,000 psi (35 kPa or 55,000 kPa)

• Sizes range from 300 hp to 50,000 hp

Single Case Compressor Centrifugal Impeller

DIFFUSERS

IMPELLERS

Introduction 1-3



• Gas flows in direction of rotating shaft

• Can be built for lower pressures only10 to 100 psi (0.7 to 6.8 Bar)

• High flow rate

• Efficient

• Not as common as centrifugals

Axial compressors

Stator Blades

Rotor

Blades

Casing

Rotor Blades

Stator

Blades

Casing

Shaft


Compressor system classifications

Single-Section, Three-Stage Single-Case, Two-Section, Six-Stage

Two-Case, Two-Section, Six-Stage

Series Network

Parallel Network

1-4 Introduction

February 26, 2001

1.2Operating

Map

From paragraph 1.1 you can extract that the two quantities flowand compression are very important when selecting acompressor for a certain application. The range of operationdepends on your process and should be covered by the selectedcompressor. While describing the operating range of aCompressor one often uses the so-called Compressor Map orPerformance Map. Measured on the axes are pressure and flow(alternative axes are discussed in 1.2.4.).

1.2.1Operating

Point

When monitoring a Compressor one can look at mechanicalquantities like vibrations and displacements or bearing and oiltemperatures, but one can also look at process quantities likegas flow and pressures. The first will give you information aboutmechanical wear and/or problems, the latter will give youprocess/operating information. Using this information in theOperating Map will result in an up-to-date point of operation ofthe Compressor, the so-called Operating Point. All processvariations will normally result in a movement of the OperatingPoint in the Compressor Map.

Pressure

FlowQ1

P1Operating Point

Introduction 1-5


1.2.2Speed /

Performanceand

ResistanceCurves

If a Compressor operates with a fixed speed, the movement ofthe Operating Point in the Compressor Map will be restricted to asingle line. This line is called the Speed Curve or PerformanceCurve belonging to this specific speed.

When operating a Variable Speed Compressor (also acompressor with inlet guide vanes, or suction throttling), theCompressor Map contains a number of Performance Curves.When changing the speed or valve position, the Operating Pointwill move from one Performance Curve to the other, creating onemore degree of freedom in the Compressor Map. The movementof the Operating Point from one Performance Curve to another isbased on the resistance felt by the compressor and follows aResistance Curve.

Pressure

Flow

Performance curvePerformance curve

for a specificfor a specific

speed N1speed N1

Resistance curveResistance curve

Q1

P1

Operating Point

NNmaxmax

NNminmin

1-6 Introduction

February 26, 2001

1.2.3Performance

Limits

Of course the movement of the Operating Point in theCompressor Map is restricted by a number of limits. The mostobvious limits in the Operating Map are the following:

Figure 2:Limits

1: Minimum Speed Limit, Throttle or Guide Vane Opening

2: Maximum Speed Limit, Throttle or Guide Vane Opening

3: Maximum Process Limiet or Discharge Pressure (Piping)

4: Maximum Load Limit (Motor Power/Current, PSteam);

5: Choke Limit (Stone Wall);

6: Surge Limit.

Qs, vol

Rc

minimum speed

maximumspeed

surge limit

stonewall or

choke limit

power limit

process limit

Developing the compressor curve

Actual availableActual available

operating zoneoperating zone

Introduction 1-7


1.2.4Axes

Compressor manufacturers use several different kinds ofCompressor Maps that differ mainly in the selection of the Axes.For the X-Axis (flow-axis) the following quantities are often used:

1: ∆Po,s: Differential Pressure [inches H2O, mbar] acrossthe Flow Measuring Device in Suction;

2: ∆Po,d Differential Pressure [inches H2O, mbar] acrossthe Flow Measuring Device in Discharge;

3: Qs Volumetric flow [ft3/hr, m3/hr] in Suction;

4: Qd Volumetric flow [ft3/hr, m3/hr] in Discharge;

5: W Mass or Net flow [lb/hr, kg/hr];

For the Y-Axis (pressure-axis) the following quantities are oftenused:

1: Pd Pressure [psi, bar, kg/cm2] in Discharge;

2: Ps Pressure [psi, bar, kg/cm2] in Suction;

3: ∆Pc Differential Pressure [psi, bar, kg/cm2] across theCompressor (∆Pc = Pd - Ps);

4: Rc Compression Ratio (Rc = Pd / Ps);

5: Hp Polytropic Head [ft lbf/lbm, kJ/kg];

6: Had Adiabatic Head [ft lbf/lbm, kJ/kg];

7: His Isentropic Head [ft lbf/lbm, kJ/kg].

The Axes that are selected by C.C.C. are discussed inparagraph 2.1.1.

1-8 Introduction

February 26, 2001

1.3SURGE

Surge is defined as "self-oscillations of pressure and flow, oftenincluding a flow reversal".


Surge description

• Flow reverses in 20 to 50 milliseconds

• Surge cycles at a rate of 0.3 s to 3 s per cycle

• Compressor vibrates

• Temperature rises

• “Whooshing” noise

• Trips may occur

• Conventional instruments and human operators

may fail to recognize surge

or “Clanking” noise


• Rapid flow oscillations

• Thrust reversals

• Potential damage

• Rapid pressure oscillations

with process instability

• Rising temperatures inside

compressor

Major process parameters during surge

FLOW

PRESSURE

TIME (sec.)

1 2 3

TEMPERATURE

TIME (sec.)

1 2 3

TIME (sec.)

1 2 3

Introduction 1-9


1.3.1Phenomenon

Figure 3:Typical Surge Cycle

A more thorough understanding of the Surge phenomenon canbe attained by observing the movement of the CompressorOperating Point on its characteristic curve during Surge.

Consider a Compressor operating in steady state at point D. Ifthe load is reduced, the Operating Point will move toward pointA, the Surge Point. If the load continues to be reduced, theOperating Point will move to the left and cross point A. At pointA, the Compressor is producing more flow than the load canabsorb. This fluid is temporarily stored in the discharge volume,but the discharge pressure cannot rise above point A. The onlyrelief for these conditions is for the Operating Point to jump topoint B. This is the flow reversal often observed during Surge.With negative flow the discharge pressure drops (traject pointsB-C). At point C we find, that the compressor is now able toovercome the discharge pressure and forward flow can bere-established, so the Operating Point jumps to point D. Now theflow is in excess of the load and the Operating Point will move upthe curve to reach point A again. This completes one SurgeCycle. The typical duration of one Surge Cycle is 0.33 to 3.0seconds.

1-10 Introduction

February 26, 2001


Developing the surge cycle on the compressor curve (1)

Qs, vol

Pd

Machine shutdown

no flow, no pressure

• Electro motor is started

• Machine accelerates to nominalspeed

• Compressor reaches performancecurve

• Note: Flow goes up faster becausepressure is the integral of flow

• Pressure builds

• Resistance goes up

• Compressor “rides” the curve

• Pd = Pv + Rlosses

A

• Compressor reaches surge point A

• Compressor looses its ability to makepressure

• Suddenly Pd drops and thus Pv > Pd

• Plane goes to stall - Compressor surges

B

• Because Pv > Pd the flow reverses

• Compressor operating point goes to point B

C

D

Pd

Pv

Rlosses

Pd = Compressor discharge pressure

Pv = Vessel pressure

Rlosses = Resistance losses over pipe


Developing the surge cycle on the compressor curve (2)

Qs, vol

Pd

Machine shutdown

no flow, no pressure

AB

C

• Result of flow reversal is that pressure goesdown

• Pressure goes down => less negative flow

• Operating point goes to point C

D• System pressure is going down

• Compressor is again able to overcome Pv

• Compressor “jumps” back toperformance curve and goes to point D

• Forward flow is re-established

Pd

Pv

Rlosses

Pd = Compressor discharge pressure

Pv = Vessel pressure

Rlosses = Resistance losses over pipe

• Compressor starts to build pressure

• Compressor “rides” curve towards surge

• Point A is reached

• The surge cycle is complete

• From A to B 20 - 50 ms Drop into surge

• From C to D 20 - 120 ms Jump out of surge

• A-B-C-D-A 0.3 - 3 seconds Surge cycle

Introduction 1-11


1.3.2Protection

Method

The consequences of Surge are severe. Besides processdisturbance and the eventual process trips and disruption, surgecan damage the Compressor. Damage to seals and bearings iscommon. Internal clearances are altered, leading to internalrecycle and thus lowering the Compressor's efficiency. OngoingSurge can result in complete destruction of the rotor.

Some surge consequences

• Unstable flow and pressure

• Damage in sequence with increasing severity

to seals, bearings, impellers, shaft

• Increased seal clearances and leakage

• Lower energy efficiency

• Reduced compressor life

Factors leading to onset of surge

• Start-up

• Shutdown

• Operation at reduced throughput

• Operation at heavy throughput with:

- Trips - Power loss

- Operator errors - Process upsets

- Load changes - Gas composition changes

- Cooler problems - Filter or strainer problems

- Driver problems

• Surge is not limited to times of reduced throughput. Surge

can occur at full operation

1-12 Introduction

February 26, 2001

This demands a reliable method of protection. As discussed in1.3.1. a combination of high discharge pressure and low flowcan result in Surge. Avoiding one or both of these situationsprevents a Compressor from going into Surge. A workingsolution can be found in a Recycle or Blow-off line. Operating avalve, positioned in this line, reduces the discharge pressure andincreases the load thus preventing Surge.

• Surge parameter based on invariant

coordinates Rc and qr

– Flow measured in suction (∆∆∆∆Po)

– Ps and Pd transmitters used to

calculate Rc

Basic antisurge control system

1

UIC

VSDS

Compressor

1

FT

1

PsT

1

PdT

• The antisurge controller UIC-1 protects the compressor against surge by

opening the recycle valve

DischargeSuction

Rc

qqrr22

• Opening of the recycle valve lowers the resistance felt by the compressor

Rprocess

Rprocess+valve

• This takes the compressor away from surge

Major Challenges of Compressor Control

• Location of the operating point

• Location of the surge limit

• High speed of approaching surge

• Control loop interactions

• Loadsharing for multiple compressor systems

• Coordinating control of compressor and driver

Antisurge Control 2-1


Chapter 2: Antisurge Control

2.1SURGE LIMIT

LINE

To be able to prevent a Compressor from experiencing Surge, one needs to know exactly where the "Surge Limit Line" is situated. This information needs to be downloaded to the Controller that controls the Recycle Valve. If this Controller knows where to find the Surge Limit Line and knows the location of the Operating Point with respect to that line, then the Recycle Valve can be opened when necessary.

Calculating the distance between the Surge

Limit Line and the compressor operating point

The Ground Rule

–– The better we can measure the distance to surge, the closer we canThe better we can measure the distance to surge, the closer we can

operate from it without taking riskoperate from it without taking risk

The Challenge

–– TheThe SSurgeurge LLimitimit LLine (ine (SLLSLL) is not a fixed line in the most commonly used) is not a fixed line in the most commonly used

coordinates. The SLL changes depending on the compressor inletcoordinates. The SLL changes depending on the compressor inlet

conditions: Tconditions: Tss, P, Pss, MW,, MW, kkss

Conclusion

–– TheThe antisurgeantisurge controller must provide a distance to surge calculation thatcontroller must provide a distance to surge calculation that

is independent of any change in inlet conditionsis independent of any change in inlet conditions

–– This will lead to safer control yet reducing the surge control margin whichThis will lead to safer control yet reducing the surge control margin which

means:means:

• Bigger turndown ratio on the compressor

• Reduced energy consumption during low load conditions on

the compressor

2-2 Antisurge Control

February 26, 2001

2.1.1Axis Selection

The Surge Limit Line is determined by a (number of) surge test(s) during the commissioning phase of a project. Information determined from this test is programmed in the Antisurge Controller. When running the Compressor, the location of the Surge Limit Line should not change when the process conditions change. This means that the selection of the Axes of the Compressor Map in which the Surge Limit Line is situated, is very significant.

If for the Y-Axis discharge pressure is used, the Operating Point will not directly react to (only) suction pressure changes. This means that the Surge Limit Line is capable of movement and that is just what we do not want. Using ∆Pc or Rc on the Y-Axis will result in a direct movement of the Operating Point when suction pressure changes. If now the temperature of the gas changes, the internal energy of the gas changes. This again not directly resulting in the movement of the Operating Point, but a moving Surge Limit Line. It becomes clear that the selection of the Axes must result in a fixed Surge Limit Line and allow only Operating Point movement during as many process changes as possible.

• Typical compressor maps include: (Qs, Hp), (Qs, Rc), or (Qs, pd)

coordinates, where:

Commonly used (OEM provided) coordinate

systems of the compressor map

QQss = Suction flow and can be expressed as= Suction flow and can be expressed as

actual or standard volumetric flowactual or standard volumetric flow

HHpp == PolytropicPolytropic HeadHead

RRcc = Compressor Ratio (p= Compressor Ratio (pdd // ppss))

ppdd = Discharge pressure of the compressor= Discharge pressure of the compressor

ppss = Suction pressure of the compressor= Suction pressure of the compressor

kkss = Exponent for= Exponent for isentropicisentropic compressioncompression

• These maps are defined for (1) specific set of inlet conditions:

ps, Ts, MW and ks



The problem with commonly used (OEM provided)

coordinate systems of the compressor map

• These coordinates areNOT invariant to suction conditions as shown

• For control purposes we want the SLL to be presented by a single

curve for a fixed geometry compressor

Developing invariant coordinates

• The following variables are used to design and to characterize

compressors

Fundamental variablesFundamental variables

characterizing compressorcharacterizing compressor

operationoperation

Hp= f0(Q, ωωωω, µµµµ, ρρρρ, a, d, αααα)

J = f1(Q, ωωωω, µµµµ, ρρρρ, a, d, αααα)

where:where:

•• HHpp == PolytropicPolytropic headhead

•• JJ = Power= Power

•• QQ = Volumetric flow rate= Volumetric flow rate

•• ωωωωωωωω = Rotational speed= Rotational speed

•• µµµµµµµµ = Viscosity= Viscosity

•• ρρρρρρρρ = Density= Density

•• aa = Local acoustic velocity= Local acoustic velocity

•• dd = Characteristic length= Characteristic length

•• αααααααα = Inlet guide vane angle= Inlet guide vane angle

• Through dimensional analysis (or similitude) we can derive two

sets of invariant coordinates

Dimensional analysisDimensional analysis

or Similitudeor Similitude

Set 1hr

qr

Ne

ααααjr

Re

Invariant coordinatesInvariant coordinates

Set 2Rc

qr

Ne

ααααjr

Re

where:where:

•• hhrr = Reduced head= Reduced head

•• qqrr = Reduced flow= Reduced flow

•• NNee = Equivalent speed= Equivalent speed

•• αααααααα = Guide vane angle= Guide vane angle

•• jjrr = Reduced power= Reduced power

•• ReRe = Reynolds number= Reynolds number

•• RRcc = Pressure Ratio= Pressure Ratio


February 26, 2001

C.C.C. generally uses Polytropic Head (Hp) versus Suction Flow squared (Qs

2). Hp is measured in [kJ/kg], [m], [ft

lbf/lbm] etc. and Qs is measured in [ft3/hr], [m3/hr], [tonnes/day] etc.

Coordinates (Hp, Qs) and (hr, qr2)

(Hp, Qs)

NOT invariant coordinates

(hr, qr2)

Invariant coordinates

where:where:

•• HHpp == PolytropicPolytropic headhead

•• QQss = Volumetric suction flow= Volumetric suction flow

•• hhrr = Reduced head= Reduced head

•• qqrr22 = Reduced flow squared= Reduced flow squared



2.1.2 Descriptionof "Surge Limit

Line"

Most limits in a process are of the "one variable" type. This means that you only need to know the value of one specific transmitter, compare it with its maximum or minimum (limit) value, and control an actuator accordingly. The Surge Limit Line is slightly different. First of all the limit cannot be crossed without potential damage to your compressor, and secondly the limit is not the maximum or minimum value of only one physical transmitter signal. In case of the Surge Limit, the limit is line in the Compressor Map, with Hp on the vertical Axis and Qs

2 on the horizontal Axis. The challenge now is to

find a way of describing the Surge Limit Line in such a way that we can see this limit as any other "one variable" type limit.

If the Surge Limit Line is a straight line through the origin, this line can be described by determining the angle (α) the line makes with the vertical axis. If the angle is known, the tangent of the angle is also known. In other words, you can describe the Surge Limit Line by determining the quotient of Qs

2 and Hp for a single point on that line. If a similar

calculation is made for a the Operating Point, the distance to the Surge Limit can be determined. Taking a closer look at the formulas for Hp and Qs

2 will lead to a surprising result.

SLL

Qs

2Qs

2

Hp

Hp

α

tanα = QH

s

pSLL

2O.P.


February 26, 2001

2.1.3Formulas for Hp

and Qs Polytropic Head: (1)

Volumetric Flow: (2)

with: (3)

and: (4)

2.1.4S-value "Ss"

As shown the quotient (called "K-value") of Hp and Qs2

determines the Surge Limit Line. In the field every Surge Limit Line has a different quotient or K-value. To create a universal way of control, C.C.C. created a patented new variable, the S-value. In C.C.C. Controllers this variable is defined as:

S-value: (5)

where: (6)

This S-value is proportional to the angular distance between the Operating Point and the Surge Limit Line. This S-value will always be 1 (one) when the Operating Point is on the Surge Limit Line! Including Formulas 1, 2, 3 and 4 in 5, gives us the following result:

(7)

H ZR

MWT

Rp avg s

c= × × ×−

0 1σ

σ

Q ZR

MWT

P

Ps

s s

o

s

= × × ×0∆

( )( )σ =

log

log

T T

P P

d s

d s

R P Pc d s=

S S KH

QSLL s

p

s O P

= = ×2

. .

KQ

H

s

pSLL

=2

S K

R

PPs

c

o

s= ×

−

×

σ

σ1

∆



In C.C.C. documentation the following reduced formula is often used:

(8)

where: (9)

and: (10)

Formulas 9 and 10 are called "Polytropic Head Reduced" and "Suction Flow Reduced".

After manipulating the formulas for Polytropic Head (1) and Volumetric Suction Flow (2), it shows that you only need to know the values of five transmitters to be able to calculate the formula for the S-value (7). These five are:

1: Differential Pressure across a Flow Measuring Device ∆Po

2: Discharge Pressure Pd

3: Suction Pressure Ps

4: Discharge Temperature Td

5: Suction Temperature Ts

2.1.5Speed

Characterizer

In case of a Variable-Speed Compressor, the Surge Points for different Speed Curves will hardly ever be located on a single straight line through the origin of the Operating Map. If calculated, the results of the surge tests for various speeds of the compressor, will give you different K-values (taking into account, that the S-value for an Operating Point moving across the Surge Limit Line has a value of 1 (one)). In other words, the K-value is not constant but is a function of the actual speed of the compressor: . This function of compressor speed is called a "Speed Characterizer" and contains the information gathered from the surge tests. The next example will illustrate this.

S KH

Qs

p red

s red

= × ,

,

2

HR

p redc

,= −σ

σ1

QP

Ps red

o

s

,

2 = ∆

K f NN = ( )


February 26, 2001

Formula 8 now changes in: (11)

The K-value and ten points for the Characterizer f(N) are entered in the Antisurge Controller. The K-value in formula 11 now mainly functions as a gain on the Speed Characterizer. In addition to the five transmitters discussed in the last paragraph, this formula needs the value of a speed transmitter to be able to calculate the S-value.

Surge test Speed N Calculated KN Constant K Characterizer f(N)

1 70% 0.50 0.5 f(0.7) = 1.0

2 80% 0.75 0.5 f(0.8) = 1.5

3 90% 1.00 0.5 f(0.9) = 2.0

S K f NH

Qs

p red

s red

= × ×( ),

,

2

Building the Surge Limit Line

•• Any curvature of the Surge Limit Line can be characterized as aAny curvature of the Surge Limit Line can be characterized as a

function of the ordinate hfunction of the ordinate hrr

qqrr22

hhrr

•• The surge parameter is defined as:The surge parameter is defined as:

•• The function fThe function f11 returns the value of qreturns the value of q rr22 on the SLL for input hon the SLL for input h rr

hhrr

qqrr,SLL,SLL

22

Sf

qs

r

r SLL

==== 1

2

(h )

,

K .



2.2SURGE

CONTROLLINE

The Surge Control Line (SCL) defines the desired minimum distance between he operating point and the Surge Limit Line (SLL). The SCL is always to the right of the SLL, as shown in the Figure below.

2.2.1Safety Margin

The Surge Limit Line is an unstable limit... when the Operating Point crosses this limit the compressor will experience (at least) one Surge Cycle. This might trip your machine or even lead to a total process shutdown. The only way to prevent this from happening is to keep the Operating Point a reasonable distance away from the Surge Limit Line. This means that the Recycle Valve as discussed in paragraph 1.3.2 needs to be opened when the Operating Point reaches a pre-selected minimum distance to surge. This minimum distance is called the "Safety Margin" and can be visualized in the Operating Map by drawing a line in front of the Surge Limit Line.

SLL

Qs

2

Hp

O.P.

SCL

b1

“Surge Control”Zone


February 26, 2001

The distance between the Surge Limit Line and the "Surge Control Line" (S.C.L.) is determined by the constant factor. The Recycle Valve will be closed as long as the Operating Point is on the right side of the Surge Control Line. When the Operating Point reaches or crosses the Surge Control Line, it enters the Surge Control Zone and the Recycle Valve will be opened. It is possible to have the S.C.L. location based upon a minimum margin (b1) plus an extra margin whenever needed.

Adding a Safety Margin (b1)

b1 = Initial Safety Marginb1 = Initial Safety Margin

b2 = Safety On Responseb2 = Safety On Response

n = number of surgesn = number of surges

b3 = Adaptive Gain Responseb3 = Adaptive Gain Response

Td0Td0 • dSdS//dtdt = derivative of S= derivative of S

SCL = Surge Control LineSCL = Surge Control Line

SLL = Surge Limit LineSLL = Surge Limit Line

qqrr22

hhrr SLLSLL

b1b1

SCLSCL

b = b1 + (b2 • n) + (b3 • Td0 • dS/dt)

• The area around the SLL is unstable

• Controlling the Operating Point at

the SLL can lead to surge

• We need to add a safety margin to

control the Operating Point in a

stable area



This extra margin is added whenever there has been adisturbance in the process which causes the Operating Pointto move towards surge... the bigger the disturbance, thefaster the Operating Point moves, the more margin is addedand the sooner the valve is opened. This movement of theOperating Point is monitored automatically by the controllercalculating a variable known as . This is known also asa derivative response or adaptive gain.

2.2.2S-value

The control action that opens the valve is of the Proportional Integral type (PI). Looking at the S-value of the Operating Point with respect to the Surge Control Line will change formula 8 to the next formula:

(12)

Notice that the S in formula 12 has no subscript "s". The difference between this S and the Ss from formula 8 is that it equals 1 (one) when the Operating Point is situated on the Surge Control Line rather than on the Surge Limit Line.

dS dt

Adaptive Gain

• b = b1 + (b2 • n) + (b3 • Td0 • dS/dt)

• b1 is the Initial Safety Margin

• b2 is the Safety On response

• b3 is the Adaptive Gain response

• When the operating point is moving

quickly towards the SLL, the

change in S with respect to time

(dS/dt) is great

• When the operating point is moving

slowly towards the SLL, the change

in S with respect to time (dS/dt) is

small

Td0 • dS/dt ~ 1

Rc

qqrr22

Td0 • dS/dt ~ 0

S KH

Qb f P

p red

s red

o= × + ×,

,

( )2 1

∆


February 26, 2001

The control action that opens the Recycle Valve uses the S-value as its Process Variable. As long as S is smaller than 1, the Output of the Antisurge Controller will be such that the Recycle valve will stay closed. When S grows bigger than 1, the Recycle Valve will be (PI) opened until S is again equal to, or less than 1. The operator interface of the Antisurge Controller does not show this S-value. Instead of that it shows, from the derived S value, DEViation.

Deviation: (13)

Deviation is 0 (zero) when the Operating Point is situated on the Surge Control Line, positive on the right, and negative on the left side of the Surge Control Line.

2.2.3Flow

Characterizer

In formula 12, the function can be manipulated tocreate different shapes for the Surge Control Line. Mostcommon is , the Control Line will then be shapedlike the one in figure 8. If , the Surge ControlLine will be parallel to the Surge Limit Line. In C.C.C.documentation this function is called .

DEV S= −1

Introducing the distance between the operating

point and the Surge Control Line

• Because S > 1 (a positive) in the Surge region (a negative situation)

We introduce parameter DEV = 1 - S

qqrr22

hhrr

SS < 1< 1

S > 1S > 1

SS = 1= 1DEV = 0DEV = 0

Surge margin (b1)

DEVDEV > 0> 0

DEV < 0DEV < 0

• The parameter DEV is independent of the size of the compressor

and will be the same for each compressor in the plant

Benefits:

• One standard surge parameter

in the plant

• No operator confusion:

• DEV > 0 Good

• DEV = 0 Recycle line

• DEV < 0 Bad

SLLSLLSCLSCL

• The parameter DEV is always the distance between the Surge

Control Line and the Operating Point

f Po

( )∆

f Po( )∆ =1f P P

o o( )∆ ∆=1

f Po4( )∆



2.3"RECYCLE

TRIP"ALGORITHM

The Speed Curves in the Compressor Map are very flat in the region of surge. The effect will be that the flow will oscillate more when the Operating Point moves closer to surge. In other words, a small change in Polytropic Head will result in more change in Flow when the Operating Point moves closer to the Surge Limit Line.

The control action that opens the Recycle Valve when the Operating Point is moving to the left of the Surge Control Line, is of the Proportional Integral type. This is a Closed Loop control action and is typically slow. Increasing the speed of control (smaller Proportional Band and/or higher Reset Rate) will have a negative outcome on the stability of the system. In the C.C.C. Antisurge Controller an extra line is added between the Surge Limit Line and the Surge Control Line.

SLL

Qs

2

Hp

O.P.

SCLRTL

RT


February 26, 2001

The extra line is called the "Recycle Trip Line" (R.T.L.). When the Operating Point crosses this line, an Open Loop response is initiated. This open loop control algorithm is added to the PI control to increase the speed of response of the control system. The objective is to prevent surge due to large or fast process disturbances. The distance between the Recycle Trip Line and the Surge Control Line is determined by the constant factor RT.

Rc

qqrr22

SLL = Surge Limit Line

RTL = Recycle Trip® Line

SCL = Surge Control Line

Output

to Valve

Time

Recycle Trip® Response

PI Control Response

Total Response



The Recycle Trip algorithm opens the Recycle Valve with astep or series of steps with a magnitude defined by formula14 and a time interval C2. Stepping up the opening of theRecycle Valve continues as long as the Operating Point stayson the left side of the Recycle Trip Line and the movement isin the direction of the Surge Limit Line (positive ).Eventually the Recycle Trip algorithm closes the Recyclevalve exponentially. This closing begins when the OperatingPoint crosses the Recycle Trip Line again but this time goingaway from the Surge Limit Line. For Series 2, 3, or 3+ thevalve will close approximately 2/3 (actually 63%) of the wayduring the first Tl (lag time) and the remainder during the nextthree Tl's for a total of four Tl‘s whether starting at 100% openor 10% open. Tl is in seconds so if Tl is set to 60, it wouldtake about four minutes for the valve to close. In Series 4, thevalve closes with an adjusted Ki (reset rate).

Step magnitude: (14)

The magnitude of each step is further subject to the restriction that the term between brackets has a value between 0 and 1. The slow closing part of Recycle Trip provides a smooth transition from the sharp action of the open loop response back to the more precise PI response.

dS dt

TIME

OUTPUT

Slow ClosingQuick Opening

Step 1

Step 2

Step 3

C2 C2 TL

|RT| = C1(Td

1•dS/dt - C

0•d

RT)


February 26, 2001

2.4"SAFETY ON"ALGORITHM

Surge could still occur if parameters are incorrectly set (or have been changed), if transmitters are improperly spanned, if impulse lines are plugged (or contain moisture), or if a process valve (Check Valve or Recycle Valve) response has deteriorated (either is stuck or trim is plugged causing reduced flow). In this event, an adaptive surge detection algorithm in the Antisurge Controller will detect the Surge Cycle and take measures to prevent this from happening again. Surge can be detected in two ways: using the "Safety On Line" (S.O.L.) or using a "Surge Signature".

2.4.1Surge Detection

using the "SafetyOn Line"

In paragraph 1.3.1 it shows that when a compressor experiences surge, the Operating Point will jump form the Surge Limit Line to the left side of the vertical axis (negative flow). In the Antisurge Controller this surge is normally detected with a detection line situated on the left side of the Surge Limit Line. This line is called "Safety On Line" (S.O.L.) and initiates the "Safety On" Response.

SLL

Qs

2

Hp

O.P.

SCLRTLSOL

SO



2.4.2Surge Detection

using a "SurgeSignature"

In some cases the flow measurement system damps the flow signal in such a way that peaks of the internal compressor flow will not be visible. This can happen when the orifice or venturi tube is located at a considerable distance from the compressor, or if the characteristics of the impulse lines to the transmitter are not optimal (too long, too small, filled with fluid etc.). This could lead to a situation that the controller does not notice the Operating Point moving to the left side of the Safety On Line, which in turn means that the controller does not detect surge. If this is the case, the controller can use an additional method of detecting surge

.

At the moment of surge, the "Rate of Change" of the flow signal and the "Rate of Change" of the pressure signal will both be maximum (either negative or positive). The Safety On algorithm can monitor these signals and look for a Rate of Change greater than a pre-selected threshold. The following modes can be used to initiate the "Safety On" Response:

1: Rapid Change in both Flow and Pressure signal.

2: Rapid Change in either Flow or Pressure signal.

3: Rapid Change in Flow signal only.

4: Rapid Change in Pressure signal only.

Surge Occurs

Flow

Discharge Pressure

Rate of Change

Rate of Change


February 26, 2001

2.4.3"Safety On"

Response

The "Safety On" Response will be triggered by one of the surge detection methods. This response will limit both the number of surge cycles which do occur and the likelihood of their recurrence. The Safety On algorithm increases the Safety Margin (initially determined by the b1 factor) each time a surge is detected. The additional safety is determined by the b2 factor. After the first surge cycle the Safety Margin is b1 + b2, after n surge cycles the Safety Margin has grown to b1 + (n x b2).

The Safety On Response allows Operations time to sit down with Maintenance, Engineering, Management and CCC if necessary in an attempt to find out why this response was triggered and to solve the associated problem. Once the determination has been made and the problem has indeed been corrected, then and only then is it safe to press the RESET key and extinguish the Safety On lamp thus resetting the actual Safety Margin to the initial Safety Margin b1.

SLL

Qs

2

Hp

O.P.

(SCL)(RTL)SOLRTL SCL

b b1 2+RT

Safety Margin = b n b1 2+ ×



2.5SUMMARY

(EXAMPLE)

This paragraph describes an example of an Operating Point moving through the Operating Map and initiating specific Antisurge Controller control actions.

When the Operating Point moves from point A to B, the Recycle Valve stays closed. At point B the valve is opened gradually on PI control. Crossing of the Recycle Trip Line (point C) will initiate the first Recycle Trip step. If the Operating Point still moves towards the Surge Limit Line after C2 seconds (point D), the second step is created. Assuming that this action turns the Operating Point around, The Valve would begin closing when the Operating Point crosses the R.T.L. again going the correct direction.

SLL

Hp

O.P.

SCLRTLSOL

A

BCDE

Qs

2

output Step 1

Step 2

B CA D E Time


February 26, 2001

Additional Control Functions 3-1


Chapter 3: Additional Control Functions

3.1Pressure

Limiting

The Antisurge Controller can also limit a maximum discharge pressure or minimum suction pressure (plus a maximum compression ratio Pd/Ps in Series 4) by increasing the opening of the recycle valve. These limiting functions open the recycle valve and does not conflict with antisurge protection.

Limiting Ps or Pd using the antisurge controller

1

UIC

VSDS

CompressorCompressor

1

FT

1

PsT

1

PdT

• The antisurge controller can be configured to limit:

• Maximumdischarge pressure (Pd)

• Minimum suction pressure (Ps)

• Both maximum Pd and minimum Ps

• This does NOT conflict with antisurge protection

DischargeSuction

3-2 Additional Control Functions

February 26, 2001

3.2Actuator Output

Conditioning

It is desirable to have the best control valve for antisurge control. Sometimes, especially during a retrofit, acquiring a new valve may be cost prohibitive. In this case, the Antisurge Controller has algorithms for actuator output conditioning that may help overcome any undesirable valve characteristics that may exists in the installed valve.

The actuator output may be modified by the following algorithms:

• Valve Flow Characterization adapts the controller to valves with non-liner characteristics.

• Valve Dead Band Compensation adapts the controller to valves with worn actuator linkages.

• The Output Clamps limit the control signal’s range. The Remote Low Output Clamp allows a companion device to increase the low clamp (and thus the minimum recycle rate).

• The Tight Shut Off Response fully closes the control valve when it is at its low clamp position and the operating point is safely to the right of the surge control line.

• Output Reverse adapts the controller to a signal to-close or signal-to-open valve.

• Output Tracking keeps the control signal equal to a speci-fied analog input whenever a discrete input is asserted.



3.2.1Valve Flow

Characterization

If your control valve exhibits inherently non-linear flow, you can render its actual flow linear with respect to the intended flow rate by selecting an appropriate Valve Flow Characterizer. The following figure illustrates the relationship between the intended recycle flow and intended valve position for each pre-defined characterizer:

For quick-opening valves, the flow is assumed to be propor-tional to the square root of the fractional valve opening. Thus the control signal is obtained by squaring the intended flow rate calculated by the control algorithms. If the intended flow is 50 percent (1/2), for example, the valve position would be 25 percent [(1/2)

2 = 1/4]. For a signal-to-open valve with a

4-to-20 mA actuator, the output signal would be 8 mA.

Conversely, the flow rate for an equal-percentage valve is assumed to be proportional to the square of the fractional valve opening. Thus the control signal is obtained by taking the square root of the intended flow rate. For example, if the intended flow is 25 percent (1/4), the valve position would be 50 percent (1/2). For a signal-to-open valve with a 4-to-20 mA actuator, the output signal would be 12 mA.

Used to improve

controllers operation

when non-linear valves

are used

Valve Flow Characterization

Control Response

(Intended Flow)

Intended

Valve

PositionValvetrim

equal percentage

Valvetrim

quickopening

• Often used on retrofits to avoid additional investment in a new valve

• Works well with equal percentage characteristics

• Works less satisfactory with quick opening characteristics

• Can be custom characterized by 10-pt linear interpolation in Series 4.

Valvetrim

linear


February 26, 2001

3.2.2Valve Dead

BandCompensation

Due to wear or design imperfections, the positioning of a con-trol valve might exhibit a dead band which must be overcome when the control action reverses direction. The Antisurge Controller can counter this effect by adding or subtracting a Valve Dead Band Bias to the intended valve position.

This bias is added when the control response is rising and subtracted when it is falling. Thus, a change in the control response’s direction produces a step change in the control signal with a magnitude equal to twice this bias.

It is better to set this bias slightly too high (as opposed to too low), so that a change in the direction of the control action will actually reverse the movement of the valve. A small antisurge PI loop dead zone should then be configured to prevent such movements from causing valve “chatter” when operating on the surge control line.

Valve dead-band compensation can be disabled by assigning its bias a value of zero.

Note: This feature will not move the actuator control signal beyond either of its output clamps.

OUT 1

Actuator Contro

l Signal

Intended Valve PositionS

igna

l

Time



3.2.3Output Clamps

The range of the actuator control signal (ACS) is defined by the Output Low Clamp and Output High Clamp. These clamps are implemented by raising or lowering the accumu-lated integral response as needed to keep the ACS within the specified range.

These clamps are entered as the minimum and maximum intended valve positions, which correspond to the highest and lowest values that would be displayed on the front-panel OUT readout. That is, the output will be constrained such that OUT never displays a number less than OUT LOW or higher than OUT HIGH.

Any Valve Open relays will be triggered whenever the actua-tor control signal is greater than the low output clamp.

Note: Because these clamps apply only when the controller is operating automatically, they do not restrict your ability to manually adjust the actuator control signal.

When setting these clamps, keep in mind that they are applied after flow characterization and valve dead band compensation but before the tight shut-off response and output reverse.

A 4-to-20 mA output is automatically generated with an offset zero, so you do not have to define that offset by setting the corresponding output clamp.

Remote LowOutput Clamp

The Antisurge Controller can be configured to use the output of another controller as its Remote Low Output Clamp when that signal is less than the low output clamp. This pre-vents the Antisurge Controller from reducing its output below that of the remote device, without risking integral windup or restricting its ability to open the valve as needed to prevent surge. In contrast to Output Tracking, this feature holds the recycle valve open far enough to satisfy both controllers.

If the Output Reverse feature is set up for a signal-to-close valve, the complement of the designated signal is used as the remote low output clamp. The remote device must then be set up to decrease its output when a higher low clamp is desired.


February 26, 2001

Note: The remote low clamp is ignored when the controller is operating in its Stop or Purge state. It does apply to manual operation, in which event raising the remote clamp can increase the displayed output (and open the valve) but lowering it will have no effect.

The remote low output clamp will be ignored if the specified signal variable is outside its transmitter testing limits.

3.2.4Tight Shut-Off

The Tight Shut-Off response can be used to fully close the recycle valve when the operating point is to the right of the Tight Shut-Off line and the output is already at its minimum clamp. This line is always to the right of the SCL

3.2.5Output Reverse

The output may be configured for a Fails-Open valve (reverse acting) or for a Fails-Closed valve (direct acting). Surge control normally uses a Fails-Open valve

3.2.6Output Tracking

In a redundant Series 3 Plus system, the redundant controller will track the output of the primary controller when the tracking discrete is asserted. In Series 4 the Output is calculated and verified in the Backup controller independently.

(Pressure)

(Flow)

SLLSCL

Tight shut-Off

Line

The Tight Shut-Off Line

defines the minimum

SCL DEViation above

which the Tight Shut-Off

Response can reduce the

recycle valve output to

zero.

The Tight Shut-Off Line

HHpp

QQss22



3.3Operating

States

There are several Operating States of the Antisurge Controller that are part of the Automatic mode of control where the Antisurge controller modulates the recycle valve

Table 3-1 Operating states

3.3.1Operating State

Transitions

Transitions between states occur as follows:

• When its compressor is stopped or idling, an Antisurge Controller operates in a Stop state that fully opens the recycle valve. If the compressor is stopped, this minimizes any reverse flow or rotation that might occur if the dis-charge check valve leaked. If it is idling, this minimizes the drive power and risk of surge.

• If the compressor is then purged, the Antisurge Controller can select a Purge state that fully closes the recycle valve so purge gas can be forced through the compressor.

• When the compressor is loaded, the Antisurge Controller selects its Run state, which reduces the recycle rate as much as possible without risking surge. It will continue to modulate that valve as needed to prevent surge with a minimum of recycling as long as the compressor is run-ning.

• While the compressor is being unloaded, the Antisurge Controller will either ramp its recycle valve open (a normal shutdown) or open it as fast as possible (an emergency shutdown).

Name Display Description

RunRUN

The compressor is loaded and the control response is being varied to prevent surge.

OFFThis compressor section is unloaded but the valve is being modulated to protect another.

StopSTOP

A normal shutdown was or is being used to idle or shut down the compressor.

ESDAn emergency shutdown was used to idle or shut down the compressor.

Purge PURGEThe compressor is unloaded but the recycle valve is fully closed.

Track TRACKActuator control signal is tracking the output of another device or controller.


February 26, 2001

The controller startup and shutdown features initiate and stop the continuous recalculation of its output signals, thus provid-ing transitions between its Run and Stop operating states. While these might be used to sequence a compressor startup or shutdown, they can alternately be set up to load and idle a running compressor.

3.3.2Manual

Operation

In Series 3 Plus, when manual operation is selected, momen-tarily pressing the Raise or Lower key will change the actuator control signal by 0.1 percent, holding either down changes it at a steadily increasing rate. The resulting value can be monitored via the OUT readout, an analog output assigned the Out function, or the Displayed OUT input regis-ter. Alternately, the control signal can be set directly by writing to the Actuator CS holding register.

In Series 4, the Manual Target is normally used to select the desired output for the actuator. Alternately, the control signal can be set directly by writing to the MODBUS Manual Target holding register if configured or through an OIS.

Although the Output Clamps do not apply in manual, the Remote Low Output Clamp does. Thus, you can raise the control signal above the high or reduce it below the low clamp parameter, but cannot reduce it below an analog low clamp.

While in manual, the controller will continue to calculate and display the deviation between the operating point and the surge control limit, so you can tell if the compressor is moving too close to surge by watching the DEV readout.

Pressure Limiting is suspended during manual operation.Initi-ating Manual

3.3.3Manual Override

Manual Override is a parameter that is used to set the how the controller will react in the Manual Operation. When the controller is in Manual and the MOR is set “OFF” (or “Soft” manual), the controller will switch back to the AUTOmatic Mode if the Operating point crosses the RTL. If the MOR were set to “ON” (or “Hard” manual), the controller will continue to stay in manual even if the compressor is surging.



Caution: CCC always recommends setting the MOR parameter to “OFF” since it disables all surge protection while the controller is in the Manual Operation

The Manual Override function is typically turned on during maintenance and troubleshooting of control inputs such as transmitters. Once the controller is placed in the Manual Operation by the operator, the maintenance technician can manipulate the input signal for loop verification and calibration without the controller accidentally switching to the Automatic Mode and opening the recycle valve. The operations personnel must monitor the DEViation during this period since there will be no surge protection by the controller. The operator can open the recycle valve to protect the compressor during a disturbance at this time.

Manual Override (MOR)

•• Manual override is normally set to OFF.Manual override is normally set to OFF.

•• Manual override must be ON for “Hard Manual” operationManual override must be ON for “Hard Manual” operation

RTLSLL SCL

Normally, the Antisurge Controller will transfer from MANUAL to

AUTOMATIC operation when the operating point of the compressor

crosses the Recycle Trip Line. The MOR function allows MANUAL to

override this feature.

dPc


February 26, 2001

3.3.4 LoopChecks With the

CompressorOn-Line

This section details the procedure for performing loopchecks on-line.

Step 1: Unlock engineering keyboard on the AntisurgeController so that parameter changes can be

made. This is accomplished as:

Step 2: Set MOR to 'On'. This is accomplished as:

MODE:A MOR 1 <enter>

Step 3: Using the front operations panel, put AntisurgeController in Manual.

Step 4: Using the 'Up' arrow on the front operations panel,open the antisurge valve to a level that will protectthe machine under all circumstances.

Step 5: Perform loop check or transmitter calibration.

Step 6: Using the front operations panel, put AntisurgeController in Automatic.

Step 7: Set MOR to 'Off'. This is accomplished as:

MODE:A MOR 0 <enter>

Step 8: Lock engineering keyboard on the Antisurge

Controller so that parameter changes can not bemade. This is accomplished as:

Note: It is possible to perform this work without using step 4,opening the antisurge valve, if so desired. This isnot advisedby CCC but can be done if process conditions warrant. Be

advised that there will be no surge control of any kind duringthis time and the machine will be completely unprotected.

Series 3 Plus Gains and Biases 4-1

S3OP_AS_GB Antisurge Application Training Manual

Chapter 4: ��

��

EXAMPLES

If the Signal on Both Transmitters are 50% and:

Pd = 100 psig SV2 = 0.50

Ps = 50 psig SV3 = 0.50

Then the Ratio of the Compressor is:

Rc = = 1.77

If the Controller Has No Gains and Biases, it will calculate RC as:

Rc = = 1.00

WHICH IS NOT CORRECT !

Transmitter Range

Pd 0-200 psig

Ps 0-100 psig

100 14.7

50 14.7

++

0.50

0.50

4-2 Series 3 Plus Gains and Biases

February 26, 2001

How to calculate Gains and Biases for this example:

Pd Gain 2 = 0.932

Pd Bias 2 = 0.068

Ps Gain 3 = 0.466

Ps Bias 3 = 0.068

Pd = Gain 2 SV2 + Bias 2

Ps = Gain 3 SV3 + Bias 3

Pd1 = 0.932 0.50 + 0.068 = 0.534

Ps1 = 0.466 0.50 + 0.068 = 0.301

Rc1 = = 0.177 = Rc

••••

200

200 +14.7

14.7

200 +14.7

100

200 +14.7

14.7

200 +14.7

••••

••••

••••

••••

∴

Series 3 Plus Gains and Biases 4-3

S3OP_AS_GB Antisurge Application Training Manual

Gains and Biases Chart

Input Channel Transmitter Gain Bias

Po(Flow)

Po,span0.999 00.0

Pd(abs)

Pd,span(abs)

Pd(gauge)

Pd,span(gauge)

Ps(abs)

Ps,span(abs)

{with Pd,span = (abs)}

Ps(abs)

Ps,span(abs)

{with Pd,span = (gauge)}

Ps(gauge)

Ps,span(gauge)

{with Pd,span = (abs)}

Ps(gauge)

Ps,span(gauge)

{with Pd,span = (gauge)}

N(Speed)

Nspan 0.999 00.0

Td(deg F)

td,span

Ts(deg F)

t s,span

(Angle)CH7 0.999 00.0

∆∆∆∆ CH1 =P

P

o

o, span

∆∆

∆∆∆∆

CH2 =P -P

P

d dL

d, span

P

P P

d span

d span dL

,

, +P

P P

dL

d span dL, +• 100

CH2 =P -P

P

d dL

d, span

P

P P P

d span

d span atm dL

,

, + +P P

P P P

atm dL

d span atm dL

++

•, +

100

CHP P

P

s SL

s span3 =

−,

P

P P

s span

d span dL

,

, +Ps

P P

L

d span dL, +• 100

CHP P

P

s SL

s span3 =

−,

P

P P P

s span

d span atm dL

,

, + +Ps

P P

L

d span dL, atm+P +• 100

CHP P

P

s SL

s span3 =

−,

P

P P

s span

d span dL

,

, +

P P

P P

atm sL

d span dL

+

+•

,100

CHP P

P

s SL

s span3 =

−,

P

P P P

s span

d span atm dL

,

, + +P P

P P P

atm sL

d span atm dL

++ +

•,

100

CH4 =−N N

N

L

span

CHt t

t

d dL

d span

5 =−

,

t

t T

d span

d span dL

,

, + +460

460

460

++ +

•T

t T

dL

d span dL,100

CHt t

t

s sL

s span6 =

−,

t

t T

s span

d span dL

,

, + +460

460

460100

++ +

•T

t T

sL

d span dL,

αααα

4-4 Series 3 Plus Gains and Biases

February 26, 2001

Series 3 Plus Antisurge Contoller Fallback Strategies 5-1

S3OP_AS_FB Antisurge Application Training Manual

��

This procedure details all the Fallback Strategies available forSeries 3 Plus Antisurge Controllers

ConstantOutput (Mode

fD31)

If the suction flow-measurement input should fail, the only

recourse is to open the antisurge valve far enough to preventsurge under the worst possible process conditions.

The corresponding fallback mode is enabled by setting Mode fD

31 to "ON". Then, when the signal to analog input CH1 is outsideits acceptable range, the controller will revert to manual controland ramp its output to the level set by COND CONST 1.

Assuming that you would want to open the recycle valve 99.9%,enter:

MODE:A fD 31 1 <enter>

COND:A CONST 1 999 <enter>

Increase compressor system reliability and

availability with fall-back strategies

• Over 75% of the problems are in the field and not in the controller

• The CCC control system has fall-back strategies to handle these field

problems

• The controller continuously monitors the validity of its inputs

• If an input problem is detected the controller ignores this input and

automatically switches to a fall-back mode

• Benefits

– Avoids nuisance trips

– Alarms operator of latent failures

– Increases machine and process availability

5-2 Series 3 Plus Antisurge Contoller Fallback Strategies

February 26, 2001

Minimum FlowControl (Mode

fD32)

Presuming that the flow input (CH1) is judged reliable but otherinput(s) are not, surge can often be prevented by maintaining the

value of the flow signal above some minimum level.

The corresponding fallback mode is enabled by setting Mode fD 32 to "ON". The controller can then resort to maintaining PV1 (the internal process variable corresponding to flow input, CH1) above the local setpoint, the initial value of which is set by COND CONST 2. That value is usually calculated as S = 1 = (CONST 2 / ∆Po',min) + b, where ∆Po',min is the value of PV1 at the desired minimum flow, which is CH1 (at that point) after a gain and bias has been applied. So, if ∆Po,min = 50" H2O and the flow transmitter span = 0 to 125" H2O, SV1 would equal 50/125 or 0.4 and since the gain and bias on CH1 is usually equal to 1 and 0 respectively, ∆Po',min = PV1 = SV1 = 0.4. So, solving for CONST 2 yields CONST 2 = (1 - b1) * (∆Po',min) or, if b1 = 20%, CONST 2 = (1 - 0.2) * (∆Po',min) = (0.8) * (0.4) = 0.32. Enable this strategy (with this example value) as:


COND:A CONST 2 320 <enter>

DefaultCompressionRatio (Mode

fD 33)

The controller can substitute a default compression ratio if thedischarge pressure input (CH2) fails.

The corresponding fallback mode is enabled by setting Mode fD

33 to "ON". The default compression ratio is set by CONDCONST 3. Enable this strategy as:


COND:A CONST 3 ### <enter>

AssumedSigma

(Mode fD 34)

If either of the temperature inputs fail (CH5 or CH6), adequatesurge protection can often be achieved by substituting aconstant value for sigma.

The corresponding fallback mode is enabled by setting Mode fD34 to "ON". The default value of sigma is set by COND CONST4. Because the calculated value for sigma can prove unreliable

during compressor start-up, CONST 4 will also be used as thestart-up value for sigma. Enable this strategy as:



Series 3 Plus Antisurge Contoller Fallback Strategies 5-3

S3OP_AS_FB Antisurge Application Training Manual

FallbackSpeed (Mode

fD 35)

The controller can substitute an assumed rotational speed whenthe speed input (CH4) fails.

The corresponding fallback mode is enabled by setting Mode fD35 to "ON". The default speed value is set by COND CONST 5.Enable this strategy as:



AssumedVane Angle(Mode fD 36)

When the chosen fa mode requires a Guide Vane Angle signal,the controller can substitute an assumed vane angle wheneverthat signal goes outside its acceptable range.

The corresponding fallback mode is enabled by setting Mode fD36 to "ON". The default vane angle is set byCOND CONST 6.Enable this fallback strategy as:


COND: A CONST 6 ### <enter>

AssumedAdjacent

Stage FlowRate

(Mode fD 37)

The controller can substitute an assumed adjacent stage flowrate if the controller fails to receive that variable via serial Port 1.

The corresponding fallback mode is enabled by setting Mode fD 37 to "ON". The default flow rate (∆Po ) is set by COND CONST 7. Enable this strategy as:



Alternate K forValve-Sharing

Controllers(Mode fD 38)

When several Antisurge Controllers are used to protect amulti-section compressor with only one antisurge valve, the

primary controller (the controller with MODE:A SS 1 enabled)can be setup to use a different Surge Limit Line Slope Coefficient(K) when it loses communication with one or more secondary

controllers (those with MODE:A SS 2 enabled).

This fallback strategy is enabled by setting Mode fD 38 to "ON".The default K value is set by COND CONST 8. Enable this

strategy as:


COND:A CONST 8 ####<enter>

5-4 Series 3 Plus Antisurge Contoller Fallback Strategies

February 26, 2001

Temperature-Based

PolytropicHead

(Mode fD 39)

If the discharge pressure input fails (CH2), it is also possible toprevent surge by using the temperature ratio method of

calculating reduced polytropic head (instead of the compressionratio method in Mode fD 33).

Since it will still be necessary to use the default value for sigma

(CONST 4), Mode fD 34 must also be enabled in order for ModefD 39 to function. Mode fD 39 will be used in preference to ModefD 33 (if both are enabled). The corresponding fallback mode is

enabled by setting Mode fD 39 to "ON". Enable this strategy as:

MODE fD 39 1 <enter>

Series 3 Plus Surge Testing (Typical Procedures) 6-1

S3OP_AS_ST Antisurge Application Training Manual

Chapter 6: ��

��

BackgroundSummary

The reason for performance testing or surge testing acompressor is to insure that the actual location of the so-called

Surge Limit Line at any given point in time is known by or can bedetermined by the antisurge controller. The primary difficulty withthis task is that the location of the Surge Limit Line (SLL) varies

with changes in inlet conditions ... suction pressure, temperature,molecular weight, etc. This method for determining the distancefrom the compressors' so-called operating point to its associated

surge point on the Surge Limit Line is discussed in detail in otherCCC texts.

In order to prevent a surge event it is necessary to know the

relative distance between the operating point and the surge pointfor that specific performance level. Performance or surge testingand the use of the patented Compressor Controls Corporation

algorithms based on reduced head versus reduced flow helpinsure that the relative distance from surge can be continuallycalculated from the required analog inputs. For a variable speed

machine that can generate an appreciable compression ratiowith variable molecular weight the following analog inputs to theantisurge controller would be required:

Analog input 1 Po,sDifferential Pressure across flowmeasuring device in the suction ofthe compressor (discharge flow can

be used with appropriate change inalgorithm)

Analog input 2 Pd Discharge Pressure, with tap as close as

possible to discharge of compressor

Analog input 3 Ps Suction Pressure, with tap as close aspossible to suction of compressor

Analog input 4 N Rotational Speed of compressor

Analog input 5 Td Discharge Temperature, with tap as closeas possible to discharge of

compressor

∆∆∆∆

6-2 Series 3 Plus Surge Testing (Typical Procedures)

February 26, 2001

Analog input 6 Ts Suction Temperature, with tap as close as

possible to suction of compressor

The choice of performance testing or surge testing a compressor

is based upon your confidence in the accuracy of themanufacturers' compressor map. This map be have beengenerated by bench testing the compressor or by computer

simulation. Bench testing is usually done with nitrogen or air,which may not be the gas you are compressing, which can leadto discrepancies between actual and predicted surge points.

Maps are also created holding suction conditions constant.Another reason for surge testing may be that the geometry of thecompressor has changed due to damage of the compressor

seals caused by repeated and numerous surge cycles during thecompressors' history, corrosion of the wheels due to causticfluids, or the deposit of waxes on the wheels.

Since the severity of a compressor surge is determined by itsperformance level (the lower the performance, the smaller thesurge event) and the speed of the compressors' operating point

when it crosses the Surge Limit Line (the lower the velocity, thesmaller the surge event), the first step in conducting aperformance or surge test would be to initially test a machine at

low performance level. The second step is going to be to insurethat you bring the operating point across the Surge Limit Line atthe lowest possible velocity. The tests would then be repeated

for progressively higher performance levels. So for a given test,you have two goals ... first, find the surge point for thatperformance level (the parameter SPEC RESP:A K, the inverse

slope of the Surge Limit Line) and second, to not damage themachine in the process. Therefor you would need to somehowbring the operating point just to the right of an unknown location

(the SLL), bring it to a complete stop and then just barely allow itto move into the SLL, at the lowest possible velocity (to insure nodamage to the machine) and then to, of course, immediately stop

the surge event ... to limit the surge event to one small cycle ofsurge. So the primary task is how to do just that, to somehowbring the operating point just to the left of an unknown location

(the SLL), bring it to a complete stop and then just barely allow itto move into the SLL. Let's examine the following techniques.



SurgeTesting in

AUTOmatic

n Hold Rotational Speed Constant

n Put Antisurge Controller in Manual

n Open Antisurge Valve 100%

n Block Compressor in Using Discharge Block Valve

n Throttle Inlet Valve to Reduce Flow

n Set Antisurge Controller Parameters for Test

n Put Antisurge Controller in Automatic

n Operating Point Will Sit on Control Line KeepingValve Open

n Slowly Reduce “K” Value, thus “artificially”Closing Valve

n Repeat Until Compressor Surges

n Recycle Trip and Safety On Responses will Bring

Controller Out of Surge After One Surge Cycle

n “K” Value on Engineering Display Represents

Location of Surge Limit Line

Step 1: First, reduce the flow somewhat through the

compressor (possibly with an inlet throttling valve),with the antisurge valve closed.

Step 2: Next, hold compressor at a minimum performancelevel with the CCC Performance Controller inMANUAL.

Step 3: Put the Antisurge Controller in MANUAL and openrecycle valve 100%.

Step 4: If possible (and / or desirable), isolate compressorfrom the process (probably with a discharge block

valve), so that the upcoming surge event and itsassociated disturbance do not upset the process.

Step 5: Disable all derivative responses (Set MODE:A fC 3and MODE:A fC 4 to OFF). This is so that during theperformance test, the location of the Surge Control

Line (SCL) cannot move automatically (fC3) and thatthe opening of the antisurge valve on Recycle Trip(RT) is a fixed amount, not altered by the speed or

velocity of the operating point (fC4).

Step 6: Disable all Fallback Strategies (Set MODE:A fD31

through fD39 to OFF).

Step 7: Set SPEC RESP:A b1 to 00.0 (this puts the SCL on

top of the SLL).


February 26, 2001

Step 8: Set SPEC RESP:A b2 to 40.0 (this will create a large

margin of safety at the moment of a Safety OnResponse).

Step 9: Set SPEC RESP:A RT to 05.0 and SPEC RESP:A SOto 10.0 (this puts the RTL and SOL just to the left ofthe SCL and SLL).

Step 10: Set SPEC RESP:A C1 to 30.0 and SPEC RESP:A C2to 0.40 (this sets the recycle trip valve opening to

exactly 30% for 0.4 second).

Step 11: Set SPEC RESP:A TL to 200 (this closes the recycle

valve 63.2% of its total in approximately 200 secondsand closes it completely in approximately 800 secondsonce the operating point returns to the right of the RTL

and SCL).

Step 12: Set PID:A PB 1 to 200 and PID:A Kr 1 to 04.0 (this

sets the PI tuning constants to average, conservativevalues).

Step 13: Set SPEC RESP:A K to .999 (this moves the SLL andtherefor the SCL out to the right as far as possible).

Step 14: Put the Antisurge Controller in AUTOmatic. DEViationwill be positive and therefore PI control will start toclose the recycle valve until DEViation is zero.

Step 15: Reduce SPEC RESP:A K by a small amount. Thisamount can vary based upon experience and

confidence, but .010 per step should be safe.DEViation will again be positive and therefore PIcontrol will start to close the recycle valve until

DEViation is again zero. Monitor vibration levels togive yourself the option of aborting the test ifexcessive levels are reached. If vibration levels are

reached that you want to avoid in the future, abort thetest at this point and use the value of SPEC RESP:A Kappearing on the engineering panel display.

Step 16: Repeat step 15 pausing to let operating point stabilizewhen DEViation becomes zero. At some point, the

entered K value will reach the value representing theactual inverse slope of the SLL. At this point, the dropin DEViation (thus crossing the RTL and SOL) will

cause a recycle trip response lasting until theoperating point, moving to the right, crosses the RTL



which is now 35% (SPEC RESP:A b1 minus SPEC

RESP:A RT) to the right of the SLL.

Step 17: Put the Antisurge Controller in MANUAL and open the

recycle valve 100%.

Step 18: Note the value of SPEC RESP:A K.

Step 19: Repeat steps 3 through 18 at several higherperformance levels. Perform a total of at least three (3)

surge tests for a variable speed machine. Instead ofstarting with the value of SPEC RESP:A K as .999,multiply the value of SPEC RESP:A K from the

previous test by 1.1 and begin with that value forSPEC RESP:A K.

Step 20: Enter the largest SPEC RESP:A K value from all testsinto the Antisurge Controller, or even better, enterSPEC RESP:A K as .500 and calculate the

appropriate function characterizer(s) required by thefA mode of the controller (MODE:A fA).

Sometimes closing the recycle valve fully may not bring thecompressor to surge. In this case, open the recycle valve inMANUAL as noted in step 3, throttle the inlet valve more,

reducing the flow, and then repeat the technique of closing of therecycle valve in AUTO. This will then bring the compressor intosurge and the procedure can be repeated for various

performance levels.

SurgeTesting inMANUAL

Under some circumstances surge testing of a compressor byclosing the recycle valve in AUTOmatic is not possible. This

applies to compressors where the recycle valve cannot beopened continually due to the absence of a cooler in the recycleline. In this case, another element such as a control valve in

discharge can be gradually closed until the compressor surges.The engineer adjusts the SPEC RESP:A K parameter so thatDEViation is equal to .000 while the discharge valve is closing.

This will require that the engineer and the manual operator of thedischarge valve are in constant radio communication with eachother. Once the compressor surges, the drop in deviation will

trigger Recycle Trip and Safety On responses and the location ofthe actual Surge Limit Line at that performance level is known asthe value SPEC RESP:A K as seen on the engineering panel

display.


February 26, 2001

Warning! Warning and Disclaimer:

Compressor Controls Corporation does not warranty thesetechniques nor accepts responsibility for their execution byany other than duly authorized employees of Compressor

Controls Corporation. These techniques are for yourinformation only and under no circumstances should theexistence of this document and its contents be construed

as a fool-proof blueprint of performance or surge testing.Do not use these techniques without consent and approvalof your senior corporate management and without the

complete knowledge and understanding of surge controltheory and the consequences of its inappropriateapplication.

SurgeTestingOn-Line

If the discharge piping cannot be isolated, surge testing must be

performed on-line. By some means the operating point must bemoved to the left, either by increasing discharge pressure ordecreasing volumetric flow rate. Typically this is done by

throttling a valve located downstream of the compressor. Byclosing this valve, the discharge pressure rises and the flow ratedecreases. Now, by artificially closing the recycle valve in AUTO

as described in the previous section, the compressor can bebrought to surge. Sometimes closing the recycle valve fully may

not bring the compressor to surge. In this case, open the recyclevalve in MANUAL as in the previous section, throttle thedischarge valve more, and repeat the closing of the recycle valve

in AUTO. This will then bring the compressor into surge and theprocedure can be repeated for various performance levels.

DeterminingSurge Line

withoutSurge

Testing

If the estimated performance curve of the compressor is to beused for establishing the Surge Line, the following procedure is

used:

The Surge Control Line parameters are set from the estimatedperformance curves or as determined in the Engineering Manual

for the job. It is important to determine that the Surge Line thusestablished is not under conservative. The actual surge lineshould not be to the right of the estimated surge line. The

operating point needs to be pushed to the left right on top of theestimated surge line and the compressor should not surge.Again, it will be easier to test this while the compressor is

isolated from the process.

Series 3 Plus Antisurge Controller Operating Principles 7-1

S3OP_AS_OP Antisurge Application Training Manual

Chapter 7: ��

SWITCHES Auto / Manual Switch

- Press to select automatic or manual operation.

Reset Safety On Switch

- Press to reset the controller for normal operation after a surgeoccurs (red light, SAFETY ON)

Display Surge Count Switch

- Press to display the number of surges in the ALT display thathas occurred since the last reset of the Safety On.

Display Limit Switch

- Press to display the limiting variable in the DEV display, thelimiting setpoint in the ALT display and which variable(Discharge or Suction) is being displayed in the AUX display.

Up-Arrow/Down-Arrow Switch

- Press to move the Antisurge output when in manual operation.

Menu Switch

- Press to display controller status or variable information in thedisplay window.

Scroll Switch

- Press to select the display variable to be viewed on the displaywindow.

7-2 Series 3 Plus Antisurge Controller Operating Principles

February 26, 2001

INDICATORS

Label Color Meaning What Can I Do?

Auto Green When lit, the controller is in the Automatic mode of operation.

You can switch to the Manual mode of operation using the Auto/Manual switch.

Manual Yellow When lit, the controller is in the Manual mode of operation. When flashing, Manual Override (MOR) is on.

You can switch to the Automatic mode of operation using the Auto/Manual switch.

RT Yellow When lit, the Recycle trip is active or the Margin of Safety is less than the RT threshold.

Nothing. This is a warning that a disturbance has occurred which the PI response could not compensate for but the RT response could. It is part of the normal operation of the controller.

SO Red When lit, the controller has detected a surge condition and has enabled a SAFETY ON response. This also means the surge count is greater than zero.

You should first determine what caused the SAFETY ON response: i.e. blocked discharge piping, damaged recycle valve, process conditions, etc. You can determine the number of surge conditions detected by pressing the Display Surge Count switch. You can reset the SAFETY ON and set the surge count to zero by pressing the Reset Safety On switch.

Limit Yellow When lit, the controller is in a limiting condition because the Discharge or Suction limiting variable is beyond their defined limiting threshold.

You can determine the value of the limiting variables by pressing the Display Limit switch. The controller will minimize the limiting condition by opening the recycle valve as needed. If possible, the process should be adjusted to prevent the limiting condition.

Tracking Green When lit, the controller is in a redundant operating mode and is tracking the active controller.

You can switch to the active operating mode by selecting this controller on the Redundant Control Selector.

TranFail Red When lit, one or more analog inputs are outside AN IN limits. It is not unusual to also see the Fallback indicator lit as well.

You can determine which analog input(s) triggered the TranFail alarm by using the MODE:D AN IN - (minus) key sequence on the Engineering Keypad. Use the scroll button to step through the successive channels.

Fallback Yellow When lit, the controller has enabled a Fallback control strategy due to the failure of analog and/or serial input(s).

You can check to see if the TranFail or ComErr indicators are lit. Then follow the procedure to determine the failed input for that indicator.

ComErr Red When lit, it indicates a serial communication error. It is not unusual to also see the Fallback indicator lit as well.

You can determine which serial input(s) triggered the ComErr alarm by using theMODE:D COMM - 2 (Serial Port 2), orMODE:D COMM - 3 (Serial Port 1) key sequence on the Engineering Keypad.

Fault Red When lit, an electronic failure has been detected within the controller. Disconnect it from the process

The controller’s output signal is totally unpredictable when the Fault indicator is lit. Process disruptions or compressor damage can result if it is not immediately disconnected from your process. You can replace this controller with your spare controller.(See the section: “Controller Change-Out”)

Series 3 Plus Antisurge Controller Operating Principles 7-3

S3OP_AS_OP Antisurge Application Training Manual

AUXILIARYWINDOW

These are what can be viewed in the Auxiliary Window display.

(Note - some of the displays may not be needed for your

application)

For Display ...Press Menu Button ...Press Menu Button

Status(RUN/STOP/OFF/PURGE

/TRACK)

Differential Pressure(ÎPo)

Polytropic Head Exponent(Sigma)

...Press Scroll Button Discharge Pressure(D Press)

Compression Ratio(Rc)

...Press Scroll Button Suction Pressure(S Press)

Temperature ratio(Rt)

...Press Scroll Button Speed(Speed)

Rotational Speed(Speed)

...Press Scroll Button Discharge Temp(D Temp)

Mass Flow Rate(Flow)

...Press Scroll Button Suction Temp(S Temp)

...Press Scroll Button User DefinedChan 7

...Press Scroll Button User DefinedChan 8

7-4 Series 3 Plus Antisurge Controller Operating Principles

February 26, 2001

February, 2001 Page 5 of 12 FM301/L (5.0)

Values above 999 display as A## and are entered as HIGH # # (102.4 displays as A2.4 and is entered as HIGH 2 4)

L®

COMPRESSOR

CONTROLS

CORPORATION

Series 3 Plus Antisurge Controller Configuration Planner

CCC No.: ____________________________ Completed By: ___________________________

Customer: ____________________________ Date: ___________________________

Tag No.: ____________________________ Software Rev.: ___________________________

S/N: ____________________________ Checksum: ___________________________

Service: ______________________________________________________________________

______________________________________________________________________

Controller ID Number (1 to 8): ________________ Computer ID Number (1 to 64): _____________

Proximity to Surge (Application Function)Application Function ________ 00, 01, 31, 33, 34, 35, 46-48, 50, 51, 61, 62, 64-69* [MODE:A fA]

Surge Limit Line Coefficient ________ normalization constant for S [SPEC:A K]Initial Surge Control Bias ________ % [SPEC:A b 1]

DEV Filter Constant ________ seconds 00.0 to 99.9 [PID:A Tf 1]Sigma Filter Constant ________ seconds 000 to 999 [PID:A Tf 2]

Constant Sigma Off / On fA modes 65 to 69 only [MODE:A fC 2]

*Available but not generally recommended application functions are 02, 32, 36 to 45, 52, 53

Input Signals∆Pc Substitution Off / High / Low High for Pd, Low for Ps [MODE:A SS 6 1]∆Tc Substitution Off / High / Low High for Td, Low for Ts [MODE:A SS 6 2]

Rotational Speed Source ________ Off for CH4 or Controller ID of source [MODE:A ANIN 4]Control Line Argument ________ CH# of analog input, Off = ∆Po [MODE:A fC 1]

Function 5 Argument ________ CH# of analog input, Off = σ [MODE:A SS 9]

Calculated FlowsFlow Element Pressure Input ________ Off or CH# of analog input [MODE:A SS 8]

Adjacent Section Controller ________ Off or A/S Controller ID for adjacent stage [MODE:A SS 5]Sidestream Flow Coefficient ________ fA 34, 35, and 64 (0.00 to 9.99) [SPEC:A C 3]

Main Flow Coefficient ________ fA 34, 35, and 64 (0.00 to 9.99) [SPEC:A C 4]Combined Flow Coefficient ________ fA 34, 35, and 64 (–9.99 to 9.99) [SPEC:A C 5]

Mass Flow Coefficient ________ 00.0 to 99.9 [COND:A β 5]Comp. Pressure Input ________ CH# of analog input for mass flow Pc [MODE:D fD 2]

Comp. Pressure Offset ________ abs. pressure when input = 0 (00.0 to 99.9) [COND:D CONST 2]Comp. Temperature Input ________ CH# of analog input for mass flow Tc [MODE:D fD 3]

Comp. Temperature Offset ________ abs. temperature when input = 0 (000 to 999) [COND:D CONST 3]

Calculated Variable DisplaysPolytropic Exponent Display Off / On Sigma [COND:D DISPLAY 1 1]Compression Ratio Display Off / On Rc [COND:D DISPLAY 1 2]Temperature Ratio Display Off / On Rt [COND:D DISPLAY 1 3]

Rotational Speed Display Off / On Speed [COND:D DISPLAY 1 4]Rotational Speed Coefficient ________ rpm 0 to 99999 [COND:D DISPLAY 1 4 HIGH]

Mass Flow Display Off / On Flow [COND:D DISPLAY 1 5]Displayed Mass Flow Coef. ________ 0 to 99999 [COND:D DISPLAY 1 5 HIGH]

Flow Variables Decimal Position 0 / 1 / 2 / 3 / 4 for Flow and UsrQ [COND:D DISPLAY 1 5 •]Mass Flow Input ________ CH# of analog input for mass flow ∆Po, Off = ∆Po,c [MODE:D fD 1]

Net Mass Flow Display Off / On** UsrQ [COND:D DISPLAY 1 7]Net Mass Flow Coef. ________ 0 to 99999 [COND:D DISPLAY 1 7 HIGH]

**If enabled, you must configure the Mass Flow Display and define the Reported Flow [COND:A f(X) 2, see page 6] and Recycle Flow [COND:D f(X) 2, see page 8] characterizers.

FM301/L (5.0) Page 6 of 12 Software Revision 754

Series 3 Plus Antisurge Controller Configuration PlannerCCC No.: __________________________ Tag No.: ___________________________ Date: ______________________________


Proximity to Surge (Continued)

Characterizing FunctionsY Coordinate Characterizer: 0.00 to 9.99 [COND:A X 1 and f(X) 1]

Rc: 0.00 ______ ______ ______ ______ ______ ______ ______ ______ 10.00f1 (Rc): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______

0 1 2 3 4 5 6 7 8 9

Reported Flow Characterizer: 0.00 to 9.99 [COND:A X 2 and f(X) 2]Rc: 0.00 ______ ______ ______ ______ ______ ______ ______ ______ 10.00

f2 (Rc): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

Rotational Speed Characterizer: 0.00 to 9.99 [COND:A X 3 and f(X) 3]N: .000 ______ ______ ______ ______ ______ ______ ______ ______ 1.000

f3 (N): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

Control Line Characterizer: 0.00 to 9.99 [COND:A X 4 and f(X) 4]X: .000 ______ ______ ______ ______ ______ ______ ______ ______ 1.000

f4 (X): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

General Characterizer: 0.00 to 9.99 [COND:A X 5 and f(X) 5]X: .000 ______ ______ ______ ______ ______ ______ ______ ______ 1.000

f5 (X): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

Fallback StrategiesDefault Output Fallback Off / On revert to manual control [MODE:A fD 3 1]

Fallback Minimum Output ________ % 00.0 for filtered value [COND:A CONST 1]Minimum Flow Fallback Off / On used when head cannot be calculated [MODE:A fD 3 2]

Default Minimum Flow ________ % [COND:A CONST 2]Compression Ratio Fallback Off / On used if Pd input fails [MODE:A fD 3 3]

Default Compression Ratio ________ 0.00 to 9.99 [COND:A CONST 3]Sigma Fallback Off / On also used as initial value during startup [MODE:A fD 3 4]Default Sigma ________ .000 to .999 [COND:A CONST 4]

Speed Fallback Off / On [MODE:A fD 3 5]Default Speed ________ % [COND:A CONST 5]

Function 5 Fallback Off / On used if MODE:A SS 9 input fails [MODE:A fD 3 6]Default f5 Argument ________ % [COND:A CONST 6]

Adj. Section Flow Fallback Off / On fA modes 34, 35, and 64 only [MODE:A fD 3 7]Default Adj. Section Flow ________ % [COND:A CONST 7]

Valve-Sharing Fallback Off / On used if valve-sharing communication fails [MODE:A fD 3 8]Alternate K ________ .000 to .999 [COND:A CONST 8]

Polytropic Head Fallback Off / On will not work unless fD 3 4 is enabled [MODE:A fD 3 9]

Operating StateGeneral Ramp Rate ________ repeats/min. for bumpless transfers [PID:A G]

Stopping Ramp Rate ________ repeats/min. 0.00 to 9.99 [COND:A LVL 3]Stop/Purge Companion ________ Off or Controller ID for S2 and S3 signals [MODE:A fB –]

Shutdown Request Off / On On to enable discrete shutdown requests [MODE:A fB 1]Purge State Off / On [MODE:A fB 2]

Safety On Auto-Reset Off / On if On, shutdown resets surge count [MODE:A fB 3]Manual While Stopped Off / On [MODE:A fB 4]

Minimum Flow and Pressure ________ % [COND:A LVL 1]Minimum Speed ________ % [COND:A LVL 2]




Surge Protection Responses

Manual OverrideManual Override Off / On Off for surge protection in manual [MODE:A MOR]

PI ResponseDEV Proportional Band ________ 006 to 999 [PID:A PB 1]

DEV Reset Rate ________ repeats/min. 00.0 to 99.9 [PID:A Kr 1]DEV Dead Zone ________ % allowable deviation (±) [PID:A r 1]

Recycle Trip®

Recycle Trip Line Distance ________ % [SPEC:A RT]Max. Recycle Trip Step Size ________ % [SPEC:A C 1]Recycle Trip Repeat Interval ________ seconds minimum time between Recycle Trips [SPEC:A C 2]

Recycle Trip Time Lag ________ seconds first-order-lag time constant [SPEC:A TL]Derivative Recycle Trip Off / On [MODE:A fC 4]

Recycle Trip Gain ________ used only if fC 4 is On [SPEC:A C 0]Recycle Trip Time Constant ________ seconds used only if fC 4 is On [PID:A Td 1]

Derivative ResponseDerivative Response Off / On [MODE:A fC 3]

Maximum Derivative Response ________ % [SPEC:A b 3]Derivative Resp. Time Constant ________ seconds [PID:A Td 0]Derivative Response Dead Zone _______ %/160 msec. threshold above which response > 0 [PID:A r 3]

The rate of decay for the Derivative Response is set by the General Ramp Rate (listed under Operating State on page 2)

Safety On®

Safety On Incremental Bias ________ % increase in surge control margin for each surge [SPEC:A b 2]Surge Relay Threshold ________ surge count to trip Surg discrete out [COND:D CONST 0]

Safety On Line Distance ________ % used by all fD 2 modes [SPEC:A SO]Surge Detection Method Off / 1 / 2 / 3 / 4 Off for SOL only, 1 for Flow and Pressure, [MODE:A fD 2]

2 for Flow or Pressure, 3 for Flow only, 4 for Pressure onlyFlow Rate of Change Thresh. ________ %/160 msec not used if fD 2 = 4 [SPEC:A A 1]Flow after Pressure Time Lag ________ seconds used only if fD 2 = 1 [SPEC:A A 2]

Pressure Rate of Change ________ %/160 msec not used if fD 2 = 3 [SPEC:A A 3]Pressure after Flow Time Lag ________ seconds used only if fD 2 = 1 [SPEC:A A 4]

Safety On Repeat Interval ________ seconds minimum time between surges [SPEC:A A 5]

Limiting Control

Discharge PressureDischarge Pressure Limiting Off / On [MODE:A MVAR 2]

Max. Discharge Pressure ________ % limiting control above this limit [COND:A SP 2]Pd Proportional Band ________ 006 to 999 [PID:A PB 2]

Pd Reset Rate ________ repeats/min. 00.0 to 99.9 [PID:A Kr 2]

Suction PressureSuction Pressure Limiting Off / On [MODE:A MVAR 3]

Min. Suction Pressure ________ % limiting control below this limit [COND:A SP 3]Ps Proportional Band ________ 006 to 999 [PID:A PB 3]

Ps Reset Rate ________ repeats/min. 00.0 to 99.9 [PID:A Kr 3]

Pressure Override Control (POC)Pressure Override Control Off / On [MODE:A SS 3]




Load SharingLoad-Sharing Controller ________ Load-Sharing Controller ID (1 to 8) [MODE:A SS 4]

Load-Sharing Gain ________ –9.99 to 9.99 [COND:A M 0]Load-Sharing Threshold ________ 0.00 to 1.99 [COND:A β 3]

Series Load Balancing Off / On* [MODE:A fC 9]Balancing Control Variable ________ Off for Rc or CH# of analog input [MODE:A fD 9]

Balancing Variable Characterizer: 0.00 to 9.99 [COND:A X 6 and f(X) 6]CV: .000 ______ ______ ______ ______ ______ ______ ______ ______ 1.000

f6 (CV): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

Recycle Flow Characterizer: 0.00 to 9.99 [COND:D X 2 and f(X) 2]CR: .000 ______ ______ ______ ______ ______ ______ ______ ______ 1.000

f2 (CR): ______ ______ ______ ______ ______ ______ ______ ______ ______ ______0 1 2 3 4 5 6 7 8 9

Port 2 Recycle Balancing Off / On if On, overrides SS 7 [MODE:A SS HIGH]Recycle Balancing Controller 1 Off / On [MODE:A SS 7 1]Recycle Balancing Controller 2 Off / On [MODE:A SS 7 2]Recycle Balancing Controller 3 Off / On [MODE:A SS 7 3]Recycle Balancing Controller 4 Off / On [MODE:A SS 7 4]Recycle Balancing Controller 5 Off / On [MODE:A SS 7 5]Recycle Balancing Controller 6 Off / On [MODE:A SS 7 6]Recycle Balancing Controller 7 Off / On [MODE:A SS 7 7]Recycle Balancing Controller 8 Off / On [MODE:A SS 7 8]

*If enabled, you must define the Reported Flow [COND:A f(X) 2, see page 6], Balancing Variable and Recycle Flow Character-izers. If enabled in fA Mode 61 through 69, you must also set the Mass Flow Coefficient [COND:A β 5, see page 5].

Loop DecouplingDecoupling Controller 1 Off / On [MODE:A SS 0 1]

Decoupling Gain 1 ________ –9.99 to 9.99 [COND:A M 1]Decoupling Controller 2 Off / On [MODE:A SS 0 2]







Decoupling Gain 8 ________ –9.99 to 9.99 [COND:A M 8]




Control ValveRecycle Valve Direction Off / On On for fails-open valve [MODE:A REV]

Valve Flow Characterizer Off / High / Low Off = linear, High = quick-open, Low = equal % [MODE:A fC 8]Remote Low Output Clamp ________ Off or CH# of analog input [MODE:A fE 4]

Output Tracking ________ Off or CH# of analog input [MODE:A fE 5]Output High Limit ________ % high limit for displayed output [COND:A OUT HIGH]Output Low Limit ________ % low limit for displayed output [COND:A OUT LOW]

Tight Shut Off Line Distance ________ % Dev threshold for fully closing valve [SPEC:A d 1]Valve Dead Band Bias ________ % added to or subtracted from Control Signal [COND:A OUT 1]

Position Failure Threshold ________ % 00.0 to 99.9 % [COND:D LVL 5]Position Failure Delay ________ seconds 0.00 to 9.99 sec [COND:D CONST 5]

Valve Sharing / Cold Recycle ControlPrimary Controller ID ________ Off or Controller ID of primary controller [MODE:A SS 2]

Valve Sharing Controller 1 Off / On [MODE:A SS 1 1]Valve Sharing Controller 2 Off / On [MODE:A SS 1 2]Valve Sharing Controller 3 Off / On [MODE:A SS 1 3]Valve Sharing Controller 4 Off / On [MODE:A SS 1 4]Valve Sharing Controller 5 Off / On [MODE:A SS 1 5]Valve Sharing Controller 6 Off / On [MODE:A SS 1 6]Valve Sharing Controller 7 Off / On [MODE:A SS 1 7]Valve Sharing Controller 8 Off / On [MODE:A SS 1 8]

For MODE:A fA = 00, the SS 1 parameters identify the Antisurge Controllers that will be monitored to determine how far to open the Cold Recycle Valve.

Analog Output 2OUT2 Assigned Variable Flow / Out / S / UsrQ [COND:D OUT 2]

OUT2 Mass Flow Coef. ________ 0 to 99.9 % [COND:D β 0]




Analog Inputs

Transmitter #1Variable ________ (normally Flow)

Measured Var. Display Off / On [COND:D DISPLAY 0 1]Measured Var. Label ________ 8 characters [COND:D DISPLAY 0 1 –]

Decimal Position 0 / 1 / 2 / 3 / 4 0 for none, 1 for 999., 4 for .999 [COND:D DISPLAY 0 1 •]Maximum Value ________ –9999 to 9999 [COND:D DISPLAY 0 1 HIGH]Minimum Value ________ –9999 to 9999 [COND:D DISPLAY 0 1 LOW]

Process Variable Bias ________ % 00.0 to 99.9 [COND:D BIAS 1]Process Variable Gain ________ .000 to 1.000 [COND:D GAIN 1]

Offset Zero Off / On On for 4-to-20 mA or 1-to-5 Vdc [MODE:D AN IN 1]High Alarm Limit ________ % 00.0 to 102.4 [MODE:D AN IN 1 HIGH]Low Alarm Limit ________ % 00.0 to 102.4 [MODE:D AN IN 1 LOW]

Transmitter #2Variable ________ (normally Discharge Pressure)





Transmitter #3Variable ________ (normally Suction Pressure)





Transmitter #4Variable ________ (normally Rotational Speed)








Analog Inputs (Continued)

Transmitter #5Variable ________ (normally Discharge Temperature)





Transmitter #6Variable ________ (normally Suction Temperature)





Transmitter #7Variable ________ (normally Guide Vane Angle)





Transmitter #8Variable ________ (normally OUT1 Loopback)





Printed in U.S.A.




COMPRESSOR CONTROLS CORPORATION4725 121st Street, Des Moines, IA 50323-2316, USA • Phone: (515) 270-0857 • Fax: (515) 270-1331

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Redundant Controller TrackingRedundant Tracking Off / On On enables tracking [MODE:D fE 1]

Modbus While Tracking Off / On Off to give controllers same ID [MODE:D LOCK 0]

Computer CommunicationsRead and Write Inhibit Off / On On inhibits reads and writes [MODE:D LOCK 1]

Write Inhibit Only Off / On On allows reads, inhibits writes [MODE:D LOCK 2]Modbus Register Scaling Off / On On to divide range by 1.024 (Port 3 only) [MODE:D LOCK 7]

Port 2 Baud Rate 2400 / 4800 / 9600 baud 9600 recommended[MODE:D COMM 2]Port 3 Format 4800 / 9600 / 19.2k baud Odd / Even / No Parity[MODE:D COMM 3]Port 4 Format 4800 / 9600 / 19.2k baud Odd / Even / No Parity[MODE:D COMM 4]

Discrete OutputsFor each output, enter one of the following functions, select + for normally de-energized operation or – for normally energized operation, and select NO for normally-open or NC for normally-closed contacts:

Auto (Automatic operation), Lim (Limiting condition), MOR (in Manual with Override enabled), Off (never tripped), On (always tripped), Open (valve Open), OutF (Output Fail), RT (Recycle Trip),

PosF (valve Position Failure), Run (Run state selected), SerC (Serial Communication error), SO (Safety On), Surg (Surge alarm count exceeded), or Tran (Transmitter failure).

Relay #1 ________ always – NO / NC Main Fault [MODE:D RA 1]Relay #2 ________ + / – NO / NC [MODE:D RA 2]Relay #3 ________ + / – NO / NC [MODE:D RA 3]Relay #4 ________ + / – NO / NC [MODE:D RA 4]Relay #5 ________ + / – NO / NC [MODE:D RA 5]

MiscellaneousRemote Parameter Switching Off / On If On, D7 loads alternate parameter set [MODE:D LOCK 3]

Input Lockout Off / On Must be OFF [MODE:D LOCK 6]Auxiliary Display Reset Off / On On to revert to Status Display after 60 sec. [MODE:D LOCK 9]

s3op - antisurge training manual

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